THE NATURAL HISTORY OF SELBORNE, 219 
On the 31st I caused the eaves to be searched, but we found 
in the nest only two callow, dead swifts, on which a second 
nest had been formed. ‘This double nest was full of the black 
shining cases of the bird-ticks. | 
The following remarks on this unusual incident are obvious. 
The first is, that though it may be disagreeable to swifts to 
remain beyond the beginning of August, yet that they can 
subsist longer is undeniable. The second is, that this uncom- 
mon event, as it was owing to the loss of the first brood, so it 
corroborates my former remark, that swifts breed regularly but 
once ; since, was the contrary the case, the occurrence above 
could neither be new nor rare. 
P.S.—One swift was seen at Lyndon, in the county of 
Rutland, in 1782, so late as the 3d of September. 
LETTER XLVIII. 
As I have sometimes known you make inquiries about 
several kinds of insects, I shall here send you an account of 
one sort which I little expected to have found in this kingdom. 
I had often observed that one particular part of a vine growing 
on the walls of my house was covered in the autumn with a 
black dust-like appearance, on which the flies fed eagerly ; and 
that the shoots and leaves thus affected did not thrive; nor 
did the fruit ripen. To this substance I applied my glasses; 
but could not discover that it had anything to do with animal 
life, as I at first expected: but, upon a closer examination 
behind the larger boughs, we were surprised to find that they 
were coated over with husky shells, from whose sides proceeded 
a cotton-like substance, surrounding a multitude of eggs. ‘This 
curious and uncommon production put me upon recollecting 
what I have heard and read concerning the Coccus vitis vinifere 
